1. Field of the Invention
In recent years, numerous fuel detergents or "deposit control" additives have been developed. These materials when added to hydrocarbon fuels employed in internal combustion engines effectively reduce deposit formation which ordinarily occurs in carburetor ports, throttle bodies, venturies, intake ports and intake valves. The reduction of these deposit levels has resulted in increased engine efficiency and a reduction in the level of hydrocarbon and carbon monoxide emissions.
A complicating factor has, however, recently arisen. With the advent of automobile engines that require the use of non-leaded gasolines (to prevent disablement of catalytic converters used to reduce emissions), it has been found difficult to provide gasoline of high enough octane to prevent knocking and the concomitant damage which it causes. The cause of the problem is the degree of octane requirement increase, herein called "ORI", which is due to deposits formed in the combustion chamber while the engine is operating on commercial gasoline.
The basis of the ORI problem is as follows: each engine, when new, requires a certain minimum octane fuel in order to operate satisfactorily without pinging and/or knocking. As the engine is operated on any gasoline, this minimum octane increases and, in most cases, if the engine is operated on the same fuel for a prolonged period will reach equilibrium. This is apparently caused by an amount of deposits in the combustion chamber. Equilibrium is typically reached after 5000 to 15,000 miles of automobile operation.
The octane requirement increase measured in particular engines used with commercial gasolines, will vary at equilibrium from 5 or 6 octane units to as high as 12 or 15 units, depending upon the gasoline compositions, engine design and type of operation. The seriousness of the problem is thus apparent. A typical 1975 or 1976 automobile with a research octane requirement of 85 when new may after a few months of operation require 97 research octane gasoline for proper operation, and little unleaded gasoline of that octane is available. The ORI problem exists in some degree with engines operated on leaded fuels. U.S. Pat. Nos. 3,144,311 and 3,146,203 disclose lead-containing fuel compositions having reduced ORI properties.
It is believed, however, by many experts, that the ORI problem, while present with leaded gasolines, is much more serious with unleaded fuel because of the different nature of the deposits formed with the respective fuels, the size of increase, and because of the lesser a vailability of high-octane non-leaded fuels. This problem is compounded by the fact that the most common means of enhancing the octane of unleaded gasoline, increasing its aromatic content, also appears to increase the eventual octane requirement of the engine. Furthermore, it was recently discovered that some of the presently used nitrogen-containing deposit control additives with mineral oil or polymer carriers appear to contribute significantly to the ORI of engines operated on unleaded fuel.
It is, therefore, highly desirable to provide fuel compositions which contain deposit control additives which effectively control deposits in intake systems (carburetor, valves, etc.) of engines operated with fuels containing them, but do not contribute to the combustion chamber deposits which cause increased octane requirements.